The present invention relates to moulding materials which can be vulcanized by means of the development of heat and which are provided with aluminum- and/or magnesium hydroxide to impart flame-resistance thereto. In another asepct, the present invention relates to a method of manufacture of these moulding materials.
Articles with flame-resistant properties are frequently manufactured in the rubber- and plastic-processing industry. This includes, among other items, flame-resistant cable jacket mixtures, conveyor belts and mixtures for use in the construction industry.
A measure of the flame-resistant properties of a mixture is represented by the LOI index (limit of oxygen index) according to ASTM 2863. The oxygen index contains the minimum concentration of xygen, expressed in percent by volume, in the mixture of oxygen and nitrogen at which the material being tested will burn the formation of flames under the conditions of the test method (ASTM 2863).
A mixture staisfies the requirements relating to flame retardation if the LOI index is over 30%.
In order to attain this numbe in the pst, flame-resistance imparting substances, namely, antimony trioxide, chloroparaffins and brominated compounds, were added to the polymer mixture. However, all these compounds are ver toxic and/or result, in the case of combustion, in very toxic decomposition products and can therefore no longer be used in view of current health and environmental regulations.
Therefore, additives such as aluminum- and magnesium hydroxide have increasingly provided themselves in recent years as non-toxic alternatives. Due to their high content of water of crystallization, which is liberated at temperature of &gt;approximately 250.degree. C., they exhibit an extinguishing action during the burning of a rubber article.
However, in order to attain flame-resistant vulcanizates which correspond to the standard, that is, an LOI index of &gt;30%, with these substances, a dosing of these substances of 120 to 150 parts by weight relative to 100 parts by weight rubber or plastic is necessary.
These large quantities have the consequence that the mechanical properties of the polymer mixtures compounded with aluminum hydroxide or magnesium hydroxide are consideraby worsened, which means that certain performance spcieficiations regarding the vulcanizate properties of these articles which are also necessary along with the flame-retarding properties are no longer attained.